Agricultural seeders are used to place seed and fertilizer in the soil to plant a crop. It is necessary to place the seed at a substantially consistent depth beneath the surface of the soil. Opener arms of various configurations typically extend downward from the seeder frame and a furrow opener is mounted on the opener arm and adapted to engage the soil to make a furrow into which the seed is deposited. Typically the furrow opener pushes soil to one or both sides and seed is deposited close behind the furrow opener so that the pushed aside soil can then fall back in on top of the seed. A packer wheel is typically provided following the furrow opener and oriented to roll over the furrow to pack the soil that has fallen hack over the seed and encourage seed germination.
The desired seed depth is typically relatively shallow, from less than one inch with some seeds and soil conditions up to three inches or more in others. Since agricultural seeders are commonly 50 or more feet wide and can include 60 or more individual furrow openers, consistently maintaining seed depth for each furrow opener in a range of fractions of an inch presents a considerable challenge.
In order to maintain consistent seed depth, it is known to pivotally attach the front end of a trailing arm to the seeder such that same extends generally rearward and downward from the frame and can pivot up and down with respect to the seeder frame. A packer wheel is then rotatably attached to support the rear end of the trailing arm. A furrow opener is attached to the trailing arm ahead of the packer wheel such that the vertical position of the bottom of the furrow opener with respect to the bottom of the packer wheel can be fixed at a desired location to set the depth of the furrow. A bias element is provided to force the trailing arm downward to push the furrow opener into the soil and force the packer wheel against the ground. These furrow opener assemblies are spaced laterally along tile width of the implement by mounting the front ends of the trailing arms to lateral frame members of the implement.
The packer wheel pushes down the soil over the seed in the furrow and the bottom of the packer wheel corresponds to the soil surface. The depth of the furrow is substantially determined by the vertical distance that the bottom end of the furrow opener extends below the bottom of the packer wheel. Such a trailing arm furrow opener assembly is disclosed for example in U.S. Pat. No. 7,159,523 to Bourgault et al. particularly in FIG. 1 thereof. U.S. Pat. Nos. 5,396,851 to Beaujot and 5,609,114 to Barton disclose trailing arm furrow opener assemblies that operate in a similar way.
A problem occurs with trailing arm furrow opener assemblies such as that of Bourgault, Barton, and Beaujot in uneven terrain where the distance between the frame and the ground varies. As the vertical distance of the frame above the ground varies the trailing arm moves up and down about its pivotal attachment to the seeder and the angle of the trailing arm changes such that the distance from the middle portion of the arm, where the furrow opener is attached, to the ground varies, and thus the actual depth of the seed furrow varies.
To improve the consistency of the furrow depth Bourgault et al. also disclose, in FIGS. 5-9 of U.S. Pat. No. 7,159,523, a trailing arm formed by upper and lower parallel arms connected at each end by front and rear links. Such a parallel link assembly has the property that the rear link is maintained in a constant horizontal and vertical orientation through the vertical range of motion without tilting forward or rearward. The front link thereof is fixed to the implement frame and the rear packer wheel and the furrow opener are fixed to the rear link. Thus as the packer wheel moves up and down relative to the frame in uneven terrain, the packer wheel and furrow opener move together vertically and so the furrow depth is maintained at a constant depth.
In some conditions it has been found when using parallel link trailing arm furrow opener assemblies that the direct relationship between vertical movement of the furrow opener and the packer wheel is detrimental to accurate seed placement. For example where the soil is hard and lumpy the packer wheel experiences excessive and erratic vertical movement. When the packer wheel rolls up and over a hard lump of soil, the furrow opener also moves up the same amount, and thus can be pulled out of the ground entirely.
In the conventional trailing arm furrow opener assembly where the furrow opener moves vertically as the packer wheel moves vertically, but a lesser distance vertically, this problem is reduced. Thus in some conditions the conventional trailing arm has advantages over the parallel link trailing arm, and in other conditions the opposite is true.